What I think is when Sid's truth is out , Roshni may ask for a divorce.DD would also hate him. There is a possibility of DD bringing in some other alliance for Roshni and Roshni would also agree for marriage in anger. She would say she don't want Sid in her life and DD may think Roshni can come out of grief if she is with someone else. At the end of the all the drama, most probably on the marriage day Roshni would realize she can't marry someone else. Then she may run away or something may happen, then Sid would find her out and they may reconcile. Then DD would also forgive Sid and SidNi can marry again.
Its just my thought, but i really think SidNi separation track would be a prolonged one and it has the potential of being high TRP gainer.